Remember that even though MDs have a larger base of legal practice rights abroad, that does not mean they will actually get licensed. Unlike the US who will license any FMG who comes over as long as they can use a stethascope, most countries have a problem of US docs taking jobs that local docs could of had. In other words, as long as you're doing mission work where someone from the US is paying you, it doesn't matter (usually) what kind of degree you have, but even with the option of practice rights, obtaining them is very difficult.
But, it's still nice to have the option though. 👍